Extruding a coating of a polyolefin or blends of polyolefins onto a substrate, such as paper or aluminum foil, to form an extrusion coated substrate, is well known in the art. Extruding multiple layers of polymers including polyolefins as well as other materials in a process known as co-extrusion is also well known. Various polyethylenes and blends of polyethylenes have been used widely as extrusion coating compositions. Such materials have also been used in coextrusion processes as the layer against the substrate so as to adhere the coating to the substrate. Unfortunately, the use of polyethylene-based coatings has several drawbacks. For example, such materials frequently lack the desired level of adhesion to typical extrusion coated substrates, especially when extrusion coating is carried out at low temperatures and/or at extremely high coating speeds. In addition, polyethylene-based coatings typically require extrusion coating temperatures that generate excessive odor and are not compatible, in co-extrusions, with some heat sensitive polymers.
Low temperature extrusion coating processes are useful when applying coextrusions with other polymers which are temperature sensitive. Low temperature extrusion coating processes are also useful when employing substrates which are temperature sensitive. Low temperature extrusion coating processes are also useful when applying polymeric coatings which contain additives which are temperature sensitive. When prior art extrusion coating materials are employed at low extrusion temperatures, they are not capable of adhering to the substrate with the desired degree of adhesion.
High extrusion coating speeds are desirable so as to enable economically attractive operation of extrusion coating equipment. High extrusion coating speeds are also desirable so as to permit the preparation of very thin extrusion coatings.
What is desired, therefore, are polyethylene-based materials which are capable of being coextruded and applied in uniform coatings to a variety of substrates employing a process which operates at temperatures below those ordinarily used for extrusion coating processes.